It all depends on what you ate…your diet might not be strict enough. If you are eating foods like rice, quinoa, nuts, etc…this could be the problem right there. Its hard to say unless you share the diet you are eating. The symptoms you mentioned sound like allergic reactions after eating certain foods.
One thing that can definitely cause die-off is if you take a large dose of antifungals, such as garlic…if it gives you flu-like symptoms, it likely is die-off.